Detection/stimulation microlead implantable in a vessel of the venous, arterial or lymphatic network

ABSTRACT

A microlead has a distal active portion formed by a microcable including an electrically conductive core coated with an insulation layer, with a plurality of exposed areas forming the stimulation electrodes. The microcable has a three-dimensional preshape inscribed in a cylindrical envelope volume so as to match the target vessel wall. The microcable includes a plurality of exposed areas regularly distributed over the circumference of the cylindrical envelope volume considered in axial projection, the exposed zones extending only over an angular sector of the microcable considered in cross section, said angular sector facing the outside of the envelope volume of the preshape.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/554,471, filed Nov. 26, 2014, is now U.S. Pat.No. 9,730,595, which is related to French Patent Application No.1361708, filed Nov. 27, 2013, the priority of which is claimed and thedisclosure of which is incorporated by reference in its entirety.

BACKGROUND

The invention relates to “active implantable medical devices” as definedby Directive 90/385/EEC of 20 Jun. 1990 of the Council of the EuropeanCommunities. This definition includes implantable devices for continuousmonitoring of the heart rhythm and to deliver if necessary electricalstimulation, defibrillation or resynchronization pulses to the heart. Italso includes neurological devices, cochlear implants, medical drugpumps, implantable biological sensors, etc.

These devices include a housing generally designated as the generatorelectrically and mechanically connected to one or more intracorporealleads provided with electrodes for contacting the tissue in which it isdesired to apply stimulation pulses and/or to collect an electricalsignal (myocardium, nerve, muscle, etc.).

The present invention more precisely relates to a detection/stimulationmicrolead intended to be implanted in the venous, arterial, or lymphaticnetworks. Performance of the stimulation of a heart chamber by animplantable lead in the coronary network will more specifically bedescribed in the present application, but this application is notrestrictive, and the microlead of the invention can be used in manyother configurations and applications permitted by its very smalldiameter.

In this example of coronary leads for stimulating a left, atrial orventricular, cavity of the heart, the lead is not inserted into thecavity to stimulate but in the coronary network, and is provided with anelectrode for contacting the wall to the epicardium at the level of theleft ventricle or of the left atrium, as appropriate. These leads thusstimulate the heart muscle via one or more point electrodes whoseposition is a function of the predefined trajectory of the cannulatedvein.

With the lead not being placed within the cavity but against a wall, theimportance of a correct orientation of the electric field generated bythe electrode must be understood, so as to ensure the orientation of theelectric field to the cardiac muscle through the vein wall, to reducethe pacing threshold and, consequently, the energy required for thestimulation.

With conventional leads, e.g. the Situs LV model sold by Sorin CRM,Clamart, France, and which is described in particular in EP 0993840 A1(ELA Medical), the lead stimulates the cavity through an annular ringelectrode blocked in the vein and contacting on the whole peripherythereof in the region of the stimulation site. The electric field isthen distributed in all directions on 360°, which corresponds to an“annular” radiation. A part of the radiation will necessarily beoriented in the direction of the heart muscle due to the constantcontact with the vein, which guarantees delivery of the stimulationenergy of the cavity where the electrode has been implanted.

However, a significant portion of the electric field is not optimallyused, as it is directed opposite to the heart muscle, which correspondsto an unnecessary energy for stimulation. Indeed, most of the electricfield is distributed in the blood, whose electrical conductivity ishigher than that of the muscle tissue, thus resulting in poorperformance for electrical cardiac pacing.

WO 02/180006 A2 describes a lead of a similar type, wherein the distalend includes an included helical preshape, the diameter of which isbetween 2.5 and 20 mm, with regularly distributed electrodes at 120° onthis preshape. The configuration of this preshape notably allows aneffective and stable contact at the interface between the lead and thewall of great diameter vessels, the helical preshape mechanicallypressing, by elasticity, the lead against the inner wall of the vessel.

A recent trend in the implantable stimulation lead in venous, arterial,or lymphatic network is the reduction in diameter, typically to adiameter of less than 2 French (0.66 mm), or reaching 0.5 French (0.17mm). This is much lower than that of conventional leads such as theSitus LV model described above, the diameter of the active portion ofwhich is of the order of 4 to 7 French (1.33 mm to 2.33 mm) or the leadssuch as those described in the WO 02/180006 A2 cited above.

The size of the lead body is indeed a factor directly related to thecapabilities of controlled guiding of the lead, for example in thecoronary venous network, which allows to select specific stimulationsites located in certain collateral veins. The very small diameteroutside the active distal end of the lead thus allows cannulation ofvery thin veins of the coronary network, so far not used because of theexcessive size of conventional coronary leads.

Such leads, which can be described as “microleads” are described forexample in EP 2455131 A1, EP 2559453 A1 and EP 2581107 A1, all three onbehalf of Sorin CRM SAS. The active portion of these microleads isconstituted by a microcable having a diameter of about 0.5 to 2 French(0.17 to 0.66 mm) having a plurality of exposed portions forming asuccession of individual electrodes constituting together a network ofelectrodes connected in series to multiply the points of stimulation ina deep area of the coronary network.

As described in particular in EP 2559453 A1 above, the very smalldiameter of the microcable can allow for introduction in a first vein(“go” vein), then by an anastomosis to a second vein (“return” vein)ascending therein. A very frequent presence of distal anastomosis in thecoronary venous network has been found, that is to say that there is atthe end of certain veins a passage to another vein, therefore with apossibility of communication between two separate veins at theanastomosis, via their respective distal ends. This makes it possible,with a single lead, to simultaneously stimulate two relatively remoteareas, because they are located in two separate veins. The double effectof the distance of these two areas and of the multiplication of pointsof stimulation in each area provides a particularly beneficial effect onthe resynchronization of the functioning of the heart.

Another advantage of the small diameter of the active part of the leadis that it avoids the blockage of a part of the blood flow in the vein,which would result in a deficiency of the venous network irrigationdownstream of the lead tip.

Reducing the diameter of the lead is nevertheless not devoid ofdrawbacks. Indeed, when the diameter of the lead is substantially lowerthan that of the vein, it is difficult to assure the permanent contactof the electrodes. The exposed portion of the microcable which forms anelectrode may thus be in an intermediate, “floating”, position in themiddle of the vein, the contact points between the microcable and thevein wall occurring on electrically isolated areas.

This is particularly true in the case of microcables passing through ananastomosis. Indeed, if the veins are of small diameter, typically lessthan 1 French (0.33 mm) in the region of the anastomosis, beyond theanastomosis they may join the coronary sinus after passing the leftventricle, and in this case their diameter increases. The very thinmicrocable which has allowed passing the anastomosis may then move intoa region of relatively large diameter, thereby with a difficulty inestablishing a stable contact between the electrodes and the vein wallin the area.

This drawback (no guaranteed contact) is the counterpart to theadvantage mentioned above to avoid the obstruction of blood flow in thevein. In contrast, the larger diameter leads including an annularstimulation ring blocked over the entire periphery of the vessel ensurecontact with the target tissue, but necessarily involve an obliterationof this vessel which can have deleterious effects. Furthermore, from theelectrical point of view, it is important to ensure, firstly, theeffectiveness of the stimulation despite a vessel having a diameterlarger than that of the stimulation microcable and, secondly, optimizedpower consumption even with a configuration of only three electrodesoriented at 120° applicable in anastomoses.

SUMMARY

Exemplary embodiments disclosed herein provide a microlead structurethat provides an effective stimulation despite a microcable diameterwell below the size of the vessel, and which:

-   -   improves contact between the vessel tissue and the microlead        stimulation electrodes;    -   directs the electric field in the direction of the target tissue        to be stimulated (heart muscle) in order to optimize the        electrical performance by not unnecessarily dissipating a        significant portion of the stimulation energy; and    -   provides distribution of the electrodes along the microlead in        well localized stimulation regions, maximizing the overall        impedance of the lead so as to reduce the stimulation threshold        and therefore the energy consumption.

Moreover, the exemplary embodiments may further provide the followingcharacteristics, from the mechanical point of view:

-   -   the microcable stimulating area has a typical outer diameter of        about 1.5 French (0.5 mm) to ensure the passage in anastomoses,        and in the microcatheter used during implantation, with an        “isodiametric” profile; that is to say an even diameter        throughout the length of the active part of the microlead;    -   the distal active part is flexible enough not to hurt the vein,        and must maintain continuous contact with the inner vessel wall        to reduce the risk of displacement or loss of stimulation; and    -   the contact force between the electrode and the inner wall of        the vessel should be as small as possible, ideally a simple        flush contact to reduce the risk of inflammation and thrombosis        between the vessel and the microcable at the contact point.

The invention discloses embodiments of a detection/stimulation microleadhaving a distal active portion constituted by a microcable of a diameterat most equal to 2 French (0 66 mm) including an electrically conductivecore coated with an insulation layer. This microcable includes at leastone stimulation zone wherein the insulation layer has a plurality ofexposed zones forming respective stimulation electrodes, and has in thestimulation area a three-dimensional preshape configured such that themicrocable matches with the target vessel wall in the stimulation area.The three-dimensional preshape can occur in a cylindrical envelopevolume whose diameter is chosen to be, in the free state of themicrocable, greater than the diameter of the target vessel.

In certain preferred embodiments of the invention, the microcableincludes, in the region of the three-dimensional preshape, at leastthree of the exposed areas—these areas being disposed at respectivelocations of the microcable located on the cylindrical envelope volume,and further, uniformly distributed on the circumference of thecylindrical envelope volume seen in axial projection. Furthermore, thesurface without insulating coating of each exposed area may be between0.1 mm² and 1 mm². In some embodiments, the surface may be less than 0.3mm².

This configuration, according to the invention, provides the followingbenefits from the electrical point of view:

-   -   The surfaces of the electrodes being reduced, the impedance Z        increases and the power decreases for a given stimulation        voltage V (optimization of the V²/Z parameter);    -   The uniform distribution of the three electrodes on 360° ensures        at least one of them is best oriented towards the excitable        tissue, thus reducing the distance to the tissue which also        reduces the power required to stimulate;    -   This best oriented electrode is in contact with the vein wall        with minimal contact pressure, which minimizes inflammation and        therefore reduces the progressive increase in the stimulation        threshold, with a favorable long-term effect on consumption; and    -   The number of three electrodes per zone as well as their        remoteness limit the efficiency losses associated with the        reducing of the current emitted because of their mutual        influences.

According to various advantageous subsidiary characteristics:

-   -   The surface without insulating coating of each exposed area may        be 0.1 mm²-1 mm²;    -   The microcable may include three exposed areas disposed at        respective locations distributed at 120° on the circumference of        the cylindrical envelope volume considered in axial projection;    -   The exposed zones may extend only over an angular sector of the        microcable considered in cross section, and the angular sector        may be outward of the envelope volume of the preshape;    -   The surface devoid of the insulating coating of each exposed        area may be less than 0.3 mm², and in other embodiments, less        than 0.1 mm²;    -   The three-dimensional preshape may be a helical preshape;    -   The at least three exposed areas may be disposed at respective        locations of the microcable regularly distributed in the        longitudinal direction on the cylindrical envelope volume;        and/or    -   The microlead may include two distinct stimulation areas        separated by an elongation and retention spacer area, shaped to        make the microlead elastically deformable in the longitudinal        direction under the effect of axial tensile/compression exerted        on the microlead in the proximal region over the elongation        area.

In one exemplary embodiment, a detection/stimulation microlead forimplantation in a target vessel of the venous, arterial, or lymphaticnetwork for stimulation of tissue in the region of the target vessel isprovided. The microlead includes a distal active portion including amicrocable of a diameter at most equal to 2 French (0.66 mm) and havingan electrically conductive core coated with an insulation layer. Themicrocable further includes at least one stimulation area having aplurality of exposed areas formed in the insulation layer forming aplurality of stimulation electrodes, wherein the surface withoutinsulating coating of each exposed area is between 0.1 mm² and 1 mm². Inpreferred embodiments, the surface is less than 0.3 mm², and in otherpreferred embodiments, less than or equal to 0.1 mm². The microcablefurther includes a three-dimensional preshape at the stimulation areaconfigured so that the microcable contacts the wall of the target vesselin the stimulation area. The three-dimensional preshape is enclosed in acylindrical envelope volume whose diameter is selected to be in the freestate of the microcable, greater than the diameter of the target vessel.The plurality of exposed areas are disposed at respective locations ofsaid microcable on said cylindrical envelope volume, these locationsbeing uniformly distributed on the circumference of the cylindricalenvelope volume considered in axial projection.

In another exemplary embodiment, a method of stimulating distinct areasof tissue through the venous coronary network through an anastomosis isprovided. The method includes introducing a microlead into the venouscoronary network through the coronary sinus and advancing the lead so asto position a first set of stimulation electrodes of the microlead in afirst vessel, a second set of stimulation electrodes in a second vessel,and an intermediate region through an anastomosis providing passage fromthe first vessel to the second vessel. The microlead comprises anelectrically conductive core coated with an insulation layer and adiameter no greater than 2 French (0.66 mm). The first set and thesecond set of stimulation electrodes are formed by exposed areas formedin the insulation layer and are separated by the intermediate region.Each of the first set and the second set of stimulation electrodes formsa stimulation area, and wherein the stimulation area comprises athree-dimensional preshape configured so that the microlead contacts thewall of the target vessel in the stimulation area. The three-dimensionalpreshape is comprised in a cylindrical envelope volume with a diameterin the free state of the microcable, greater than the diameter of thetarget vessel. The stimulation electrodes in each stimulation area aredisposed at respective locations of said microlead on said cylindricalenvelope volume, these locations being uniformly distributed on thecircumference of the cylindrical envelope volume in axial projection.The method further includes providing stimulation through the targetvessels by the first and second set of electrodes.

DRAWINGS

Further features, characteristics and advantages of the presentinvention will become apparent to a person of ordinary skill in the artfrom the following detailed description of preferred embodiments of thepresent invention, made with reference to the drawings annexed, in whichlike reference characters refer to like elements and in which:

FIG. 1 generally illustrates the myocardium, with the main veins of thecoronary network in which a lead according to the invention has beenintroduced for the stimulation of the left ventricle.

FIG. 2 illustrates the end portion of the microcable according to theinvention for the multi-zone stimulation.

FIG. 3 is an end view, in an axial direction, of the microlead of theinvention introduced into a vessel of the coronary network, showing themethod by which the contact is provided at the stimulation site, bywhich the electrical field can be specifically distributed in directionof the heart muscle.

DETAILED DESCRIPTION

An exemplary embodiment of the microlead of the invention, applied tothe stimulation of a heart chamber by a lead implanted in the coronarynetwork, will now be described. As indicated above, this application isnot restrictive, and the microlead of the invention can be used in manyother applications in view of its ability to be implanted in the deepvenous, arterial or lymphatic networks.

FIG. 1 generally illustrates the myocardium and the main coronaryvessels of the coronary network, wherein a lead according to theinvention is introduced to stimulate the left ventricle. This lead isendocardially implanted in the venous coronary network via the superiorvena cava, the right atrium and the input of the venous coronary sinusCS. The venous coronary network then develops into several branches fromthe great cardiac vein GVC, these branches including the posterolateralvein VPL, the lateral vein VL, the anterolateral vein VA and theposterior vein VP.

Reference 10 generally refers to the lead according to the invention,which includes in its active part a microcable 12 whose distal part isshown in FIG. 2 in isolation. The lead 10 further includes, in itsproximal region, a microcatheter 18 entering the coronary sinus and thegreat cardiac vein GVC to the opening of the anterolateral vein VA.

The microcable 12 is introduced into the anterolateral vein VA andcarries a plurality of stimulation electrodes 14 to stimulate the leftventricle from multiple sites in this vein VA. The microcable 12 alsocarries, at a distance from the electrodes 14, another set of electrodes16 to stimulate the left ventricle from a different vein, e.g. via aposterolateral vein VPL via a communication by an anastomosis 22connecting the anterolateral vein VA and the posterolateral vein VPL.The microcable crosses this anastomosis 22 and the more distal regionsof both VA and VPL veins along an intermediate portion 20 free of theelectrodes.

With this configuration, it is possible not only to stimulate the leftventricle at several points of one of the veins (because of themultiplication of the electrodes 14 or 16), but also to provide tworelatively remote stimulation areas, respectively the area of theelectrodes 14 and the area of the electrodes 16, located in twodifferent proximal regions of the two veins in which it would bedifficult to stabilize or fix conventional left ventricular pacing leadsbecause of the large diameter of the mouth of these veins.

FIG. 2 describes the distal active portion of the microcable 12, withthe first set of electrodes 14 and the second set of electrodes 16, thetwo sets being separated by the intermediate portion 20.

The microcable 12 includes an electrically conductive core provided withan insulating coating on its entire length, except for occasionallyexposed areas constituting the detection/stimulation electrodes 14 and16. In regards to the structure of the microcable 12, the core thereofis preferably a multi-stranded structure in which each strand ispreferably made of nitinol (NiTi alloy) or MP35N-LT (35% Ni, 35% Co, 20%Cr and 10% Mo), materials whose main advantage is their extreme fatigueendurance, with a sheath coating of platinum-iridium or tantalum (forradiopacity and biostability). Such a structure allows optimizing theresponse to the requirements of corrosion resistance at the electrodes,and of endurance against cardiac movements. These microcables areavailable for example from the company Fort Wayne Metals Inc., FortWayne, USA.

The core wire is coated with a thin insulation layer, on the order of 25microns thick, for example by coextrusion of the conductor or by a heatshrinkable tube. The insulator may be a thin layer of parylene (e.g.,type C). In this case, windows of varying complexity are created alongthe microcable, e.g. by plasma ablation, to form the electrodes 30. Toimprove electrical performance, these areas can further be coated, forexample with titanium nitride. In other embodiments, the insulator maybe a polyurethane tube interrupted at the locations of electrodes 14 and16. In other embodiments, the insulator may be one or more layersconsisting of tubes made of PET (polyethylene terephthalate),fluoropolymer, PMMA (polymethyl methacrylate), PEEK(polyetheretherketone), polyimide or other suitable similar material.

A particular advantage of this structure results from the very flexibleand floating (floppy) characteristics of the microcable, which providesexcellent atraumaticity. Such a microcable does not attack the tissueand thus preserves the cells adjacent to the electrodes.

In the configuration described herein, the microcable includes a singleconductor, so that the exposed regions form electrodes, which, from theelectrical point of view, are connected together and are at the samepotential. This monopolar configuration is however not limiting, and theinvention is equally applicable to a multipolar lead, with a microcableincluding a plurality of separate conductors electrically insulated fromeach other, for example as a bundle of insulated conductors strandedtogether, each being provided with one or more exposed areas formingrespective electrodes.

The microcable has a three-dimensional preshape at the location of theelectrodes 14 which form a first stimulation zone ZS1, and at thelocation of the electrodes 16 which form a second stimulation zone ZS2.This preshape is designed to promote the electrode contact with thevessel wall, and thus the electrical performance.

The two stimulation areas ZS1 and ZS2 preferably have an identicalconfiguration. The three-dimensional preshape of the microcable 12 tothe location of each stimulation area is inscribed in a cylindricalenvelope volume 24 whose diameter D is chosen to be, in the free stateof the microcable, greater than the diameter of the target vessel. Insome embodiments, the diameter D of the cylindrical envelope volume maybe at least twice the diameter of the target vessel. For example, thestimulation area may have a diameter of 12 mm for a microlead to beimplanted into a target vein of 2 to 6 mm in diameter.

Preferably, the three-dimensional preshape is a helical one in thecylindrical envelope 24. Thus, when the lead is inserted into the vein,the helical shape of the microcable is naturally press against thewalls, ensuring a permanent contact. Furthermore, the three exposedareas 14 or 16 are, in the longitudinal direction, arranged atrespective locations evenly distributed over the volume of thecylindrical envelope 12 of the microcable.

To ensure the stability of the assembly, a preshape 26 is added to theintermediate portion 20 free of the electrode, so as to constitute anelongation area ZEL to facilitate elongation of the lead in the axialdirection (arrows 28), especially during the stresses exerted on themicrocable with each heartbeat, or if the patient moves and performsfurther movement (lifting of the arm, etc.). These efforts will beabsorbed by deformation of the elongation area ZEL without moving thestimulation areas ZS1 and ZS2, so with no effect on the positioning ofthe electrodes. The preshape 26 of the elongation area ZEL is selectedso that its diameter is smaller than the diameter of the target vein,and its shape is selected so as to have a greater flexibility in axialdirection than of the preshapes of the stimulation zones ZS1 and ZS2.This elongation area also provides a complementary retention function ofthe microlead into the vein.

FIG. 3 is an end view, in an axial direction (shown in section), of anembodiment of the microlead in the stimulation area ZS2, this microleadbeing inserted into a vessel of the coronary system. In this view, itcan be seen that there are three electrodes 16 in the stimulation areaZS2 (it is the same for the electrodes 14 of the stimulation area ZS1)distributed at 120°, in axial view, on the surface of the envelopevolume 24. This configuration ensures contact at all times of at leastone of the electrodes (the electrode located at the bottom left in theexample of FIG. 3) with the inner vessel wall 30, regardless of theangular configuration of the preshape carrying the electrodes withrespect to the vein 30.

Indeed, from the anatomical point of view, the interface between thecardiac muscle 32 and the coronary vein 30 does not appear as a flatsurface, but with a lateral flange 34 (fatty deposits) ensuring that theextent of contact between the vein 30 and the cardiac muscle 32anatomically occurs on an angular sector. This increases the chances ofcontact of at least one of the electrodes 16 with the inner wall of thevein 30 in the region of this angular sector, thereby allowing a directtransmission of electrical energy from the electrode 16 to the heartmuscle 32.

The number and distribution of electrodes 16 (three electrodes, placedat 120°) are considered preferred but are not a limitativeconfiguration. There could be a higher number of electrodes, for examplefour in number, leading to a superior warranty of contact with the wallof the vein, but at the cost of higher electrical losses. In this case,if only one electrode is in contact with the heart tissue,three-quarters of the energy will be dissipated in the blood and not tothe heart muscle against only two thirds in the case of a threeelectrode configuration.

Furthermore, the exposed areas constituting the electrodes 14 or 16extend only over an angular sector of the microcable considered in crosssection. These are “segment” electrodes rotated outwardly of theenvelope volume of the preshape 24, so in the direction of the innervessel wall 30, in the area wherein the possibility of contact with thewall is maximum.

The exposed surface of each electrode 14 or 16 is typically constitutedby a hole formed in the insulating material of the sheath to a diameterof 0.2 mm, for example by firing a low-power laser to locally melt theinsulation of the microcable without damaging the core conductorthereof. The total area of all the electrodes 14 of the stimulation areaZS1 (or of all electrodes 16 of the stimulation area ZS2) is between 0.3mm² and 3 mm² (with certain embodiments having three electrodes eachwith an area of between 0.1 mm² and 1 mm²), a value from several timeslower than conventional leads such as the Situs LV model initiallydescribed, the surface of the annular electrode is about 6 mm².

It is thus possible to stimulate the heart muscle by concentrating theelectric field on a small area corresponding to the small exposedsurface area, resulting in a significant increase in the impedance ofthe lead leading to a much lower energy delivered by the generator ateach stimulation pulse, for the same or even greater efficacy.

What is claimed is:
 1. A detection/stimulation microlead forimplantation in a target vessel for stimulation of tissue in a region ofthe target vessel, the microlead comprising: an electrically conductivecore coated with an insulation layer; a plurality of exposed areasformed in the insulation layer and comprising a plurality of stimulationelectrodes; and a three-dimensional preshape formed at one or more ofthe plurality of exposed areas, the three-dimensional preshapestructured such that the exposed area of the microlead contacts a wallof the target vessel, wherein the three-dimensional preshape isstructured so that portions having a largest diameter contact the vesselwall, the largest diameter being greater than a diameter of the targetvessel; and wherein the plurality of electrodes are disposed atrespective locations of said microlead on said three-dimensionalpreshape, these locations being uniformly distributed on a circumferenceof the three-dimensional preshape considered in an axial projection; andwherein the plurality of electrodes are included within two distinctstimulation areas separated by an intermediate region.
 2. The microleadof claim 1, wherein the plurality of electrodes are uniformlydistributed on a circumference of the three-dimensional preshapeconsidered in an axial projection.
 3. The microlead of claim 1, whereinthe largest diameter is at most equal to 2 French (0.66 mm).
 4. Themicrolead of claim 1, wherein the plurality of electrodes have an areabetween 0.1 mm² and 1 mm².
 5. The microlead of claim 1, wherein thethree-dimensional preshape is a helical preshape.
 6. The microlead ofclaim 1, wherein the plurality of electrodes are disposed at respectivelocations of the microlead regularly distributed in a longitudinaldirection on a cylindrical envelope volume.
 7. The microlead of claim 1,wherein the intermediate region comprises a retention and elongationarea, elastically deformable in a longitudinal direction under an effectof tensile/compression axial stress exerted on the microlead in aproximal area with respect to the elongation area.
 8. The microlead ofclaim 7, wherein the intermediate region comprises a preshape formed inthe microlead in a free state.
 9. The microlead of claim 8, wherein thepreshape of the intermediate region is selected to have a diametersmaller than the diameter of the target vessel.
 10. The microlead ofclaim 1, wherein three-dimensional preshape has a diameter of at leasttwice the diameter of the target vessel.
 11. A method of stimulatingdistinct areas of tissue via a venous coronary network, comprising:introducing a microlead into the venous coronary network through acoronary sinus; advancing the microlead so as to position a first set ofstimulation electrodes of the microlead in a first vessel, a second setof stimulation electrodes in a second vessel, and an intermediate regionthrough an anastomosis providing passage from the first vessel to thesecond vessel, wherein the microlead comprises a three-dimensionalpreshape structured so that the first set of electrodes and the secondset of electrodes contact a wall of a target vessel and so that portionshaving a largest diameter contact the vessel wall, the largest diameterbeing greater than a diameter of the target vessel; and providingstimulation through the target vessels by the first and second set ofelectrodes.
 12. The method of claim 11, wherein the plurality ofelectrodes are disposed at respective locations of said microlead onsaid three-dimensional preshape, these locations being uniformlydistributed on a circumference of the three-dimensional preshapeconsidered in an axial projection.
 13. The method of claim 11, whereinthe first set and the second set of stimulation electrodes are separatedby the intermediate region and the intermediate region is elasticallydeformable in a longitudinal direction under an effect oftensile/compression axial stress exerted on the microlead in itsproximal area with respect to the elongation area.
 14. The method ofclaim 12, wherein the intermediate region of the microlead comprises apreshape formed in the microlead in a free state, wherein the preshapeof the intermediate region of the microlead is selected to have adiameter smaller than the diameter of the target vessel.
 15. The methodof claim 11, wherein the first set and the second set of stimulationelectrodes each have an area between 0.1 mm² and 1 mm².
 16. Adetection/stimulation microlead for implantation in a target vessel forstimulation of tissue in a region of the target vessel, the microleadcomprising: a three-dimensional helical preshape at a stimulation area,the stimulation area comprising a plurality of electrodes, and thethree-dimensional helical preshape configured such that the microleadcontacts a wall of the target vessel in the stimulation area; whereinthe three-dimensional helical preshape is structured so that portionshaving a largest diameter contact the vessel wall, the largest diameterbeing greater than a diameter of the target vessel; and wherein theplurality of electrodes are disposed at respective locations of saidmicrolead on said three-dimensional helical preshape.
 17. The microleadof claim 16, wherein the three-dimensional preshape has a diameter of atleast twice the diameter of the target vessel.
 18. The microlead ofclaim 16, wherein the largest diameter is at most equal to 2 French(0.66 mm).
 19. The microlead of claim 16, wherein the plurality ofelectrodes have an area between 0.1 mm² and 1 mm².